Control of the localized electrochemical dissolution of solid-state sintered silicon carbide – SiCECM

固态烧结碳化硅陶瓷(SSIC)因其良好的机械性能、摩擦学性能和耐腐蚀性能，被广泛应用于电厂、化工等领域的机械密封或阀门。然而，它们的高硬度和高抗压强度给机械成形和表面处理带来了困难。高熔点会通过电火花烧蚀或激光烧蚀来影响热加工。由于受机械和热性能的影响，电化学加工(ECM)是一种很有前途的选择。但目前在用于定向成形和表面结构的适用加工参数方面存在严重限制。两个申请者自己的初步研究证明了SSIC的阳极溶解的基本解决方案，该SSIC具有足够高的导电性，可以满足所需的电荷交换。形成钝化层，在足够高的电势下，通过电解形成相当数量的氧，从而发生介电穿透。关于氧化层的形成和溶解、可能的副反应和pH值的变化以及对钝化层不稳定性的影响，目前还没有更详细的研究，也没有统一的热力学描述。此外，由于SSIC的半导体特性，焦耳加热对去除速率的影响还没有被观察到。JET-ECM可以在足够高的电压和单独的电解液组成下，通过强聚焦电流来实现SSIC的高局域化溶解，从而为表面结构的研究提供了一种很有前途的方法。然而，可预测的烧蚀几何形状和局部焦耳加热对电流效率的影响尚不清楚。为了在足够小的时间尺度和几何维度上分析相关的相互作用的场量和场量分布，并了解它们之间的关系，数值模拟模型显得有用和必要。主要目的是研究工艺输入参数对SSIC阳极溶解的影响，为Jet-ECM模拟辅助微结构设计奠定基础。为此，我们将研究在较低电势下的跨被动突破和去除连续性。在微毛细管池中获得的基本知识应为Jet-ECM工艺参数定标模拟模型的开发提供必要的输入参数。应对氧的析出和碳的反应进行量化，以求出硅和碳的氧化态及其化学计量比，并控制去除几何形状。

Due to their very good mechanical, tribological and corrosion-resistant properties, solid-state sintered SiC ceramics (SSiC) are used, for example, as mechanical seals or valves in power plant construction and chemical industry. However, their high hardness and compressive strength make mechanical shaping and surface treatment difficult. The high melting point impairs thermal machining by spark erosion or laser ablation. Electrochemical machining (ECM) represents a promising alternative due to the subordinated influence of mechanical and thermal workpiece properties. But there are currently severe limitations with regard to applicable machining parameters for targeted shaping and surface structuring. Own preliminary studies of both applicants prove basic solutions for anodic dissolution of SSiC with sufficiently high electrical conductivity for the required charge exchange. Passivating layers are formed, and dielectric breakthrough occurs with considerable formation of oxygen through electrolysis at sufficiently high electric potential. More detailed investigations into oxide layer formation and dissolution, possible side reactions and pH value changes as well as effects on the instability of the passive layer are not yet known, and there is no uniform description of the ECM in thermodynamic imbalance. In addition, the observed influence of Joule heating on the removal rate due to the semiconductor properties of SSiC has not yet been investigated. Jet-ECM enables the application of sufficiently high voltages and individual electrolyte composition for the dissolution of SSiC with high localization through strongly focusing the current flow and thus represents a promising method for researches on surface structuring. However, predictable ablation geometries and the impact of local Joule heating on the current efficiency are not known. In order to analyze relevant, interacting field quantities and field quantity distributions in sufficiently small time scales and geometry dimensions and to understand their relationships, numerical simulation models appear useful and necessary. The main goal is the fundamental research of the influences of process input parameters on the anodic dissolution of SSiC for simulation-assisted design of micro-structuring by Jet-ECM. For this purpose, the trans-passive breakthrough and removal continuity at lower electric potential will be investigated. Basic knowledge gained in a micro-capillary cell shall provide the necessary input parameters for the development of a simulation model for the scaling of Jet-ECM processing parameters. The oxygen evolution and carbon reaction shall be quantified in order to derive the oxidation states of Si and C and their stoichiometry and to control the removal geometry.